1. Field of the Invention
The present invention relates to a numerically controlled grinding machine capable of automatically determining a timing for dressing a grinding wheel and other grinding data.
2. Description of the Prior Art
In grinding a workpiece, each ground section (stage) of the workpiece is finished by one grinding cycle comprising a series of grinding steps, i.e., a rapid feed, a rough grinding, a fine grinding and a finish grinding, which differ from each other in an infeed rate and a grinding accuracy.
The grinding cycle for grinding each ground section of the workpiece is divided into two stages, if a desired finished accuracy can not be obtained. This judgment is carried out based upon the type of the grinding wheel employed, the grinding allowance and required surface accuracy of the ground section. And a grinding wheel dressing step is inserted between the two divided stages.
In grinding a workpiece having a plurality of ground sections, such as a multi-stage spindle, the grinding wheel may be dressed after finishing one of the ground sections before starting grinding the next one of the ground sections, because the ground sections are ground respectively in different grinding modes, such as a traverse grinding mode and a plunge cut grinding mode, and an amount to be ground by the grinding wheel increases with respect to the number of the ground sections.
However, no criterion has been established for deciding whether or not the grinding cycle must be divided into two stages and the grinding wheel dressing step must be inserted between the two divided stages, or whether or not the grinding wheel dressing step must be inserted between the grinding cycles for grinding the successive ground sections in grinding a workpiece having a plurality of ground sections. Such a decision has been dependent on the experience of the operator. Accordingly, there is such a problem that a frequency of the grinding wheel dressing is dependent on the judgment of the respective operators and as a result a machining time and a finished accuracy of the workpiece are dependent on the skill and experience of the respective operators.
There is known a grinding data producing apparatus capable of producing grinding data necessary for the automatic operation of a numerically controlled grinding machine, including grinding conditions, such as a grinding infeed rate, a rotating speed of a workpiece, grinding modes, a grinding sequence, grinding wheel dressing conditions and a grinding wheel dressing interval.
This grinding data producing apparatus determines the grinding data by a procedure shown in FIG. 14.
This procedure requires the operator to decide in step S10 after the determination of grinding modes whether or not the grinding cycle is to be divided to insert the grinding wheel dressing step between the two divided grinding stages.
The operator determines whether or not each ground section can continuously be ground and finished without dressing the grinding wheel during the grinding cycle, on the basis the abrasion of the cutting face of the grinding wheel that is empirically estimated by the operator according to the grinding cycle.
After the determination of a grinding sequence specifying the grinding order among the ground sections, the operator decides empirically in step S20 whether or not the continuous grinding of all the ground sections of the workpiece is possible without an intermediate dressing of the grinding wheel.
If it is decided that the grinding of all the ground sections is possible without the intermediate grinding wheel dressing, the operator decides empirically the number of workpieces that can be finished without the grinding wheel dressing, namely, a grinding wheel dressing interval.
Since the known grinding data producing apparatus requires decisions to be made by the operator, full automatic determination of the grinding data is impossible.